In the processing of aluminum flat-rolled products such as sheet or plate, typical practices include hot rolling the cast ingot into thinner pieces. This hot rolling might produce plate product, sheet product and/or coil stock that can then be later cold rolled to final gauge or be sold directly off the hot mills. In the hot rolling operation, it is essential to provide a lubricating and cooling medium at the roll bite that will allow friction control, remove heat from the rolls, control the temperature of the metal workpiece and provide an environment that controls the transference of aluminum to the rolls and then back onto the strip. This phenomenon is called "pickup". Lubricating coolants used in the aluminum industry can be dispersions of oil-in-water. In the case of dispersions stabilized with surfactants, they are called emulsions. In service, these dispersions and emulsions become contaminated with aluminum wear debris as a consequence of the action of the hard steel rolls sliding over the soft aluminum during the rolling operation. Also, the chemically active ingredients in the rolling oil, typically fatty acids, become chemically combined with the nascent aluminum and, while forming metallic soaps, become used up, thus lowering the lubricating effectiveness of the oil in the emulsion or dispersion. When the contamination due to metallic particles and the reduction of the chemically active fatty acids in the dispersion or emulsion becomes too great, the performance of the emulsion with respect to its ability to provide the proper friction in the roll-bite, its ability to control pickup and its ability to remove heat satisfactorily, deteriorates to unacceptable levels.
Until now, the only way to reestablish the desired performance is to discard the in-service lubricant now called "spent" lubricant, and make up the dispersion or emulsion with new water and oil. This is a costly procedure and, additionally creates a disposal issue with regards to the spent dispersion or emulsion.